1. Field of the Invention
The present invention generally relates to a light-emitting element array having an element-separating structure in which a semiconductor layer formed on a substrate is divided into a plurality of regions (element regions).
2. Description of Related Art
An array of light-emitting elements is a device in which a plurality of light-emitting elements is arranged in a line at equal intervals. An LED array is one such array of light-emitting elements and employs LEDs (light-emitting diodes) as a light-emitting element. An LED array is used as a light source in an optical printer that is based on electrophotography.
FIG. 6 illustrates a pertinent portion of a conventional LED array.
Referring to FIG. 6, an LED array 110 employs a matrix type wiring arrangement that reduces the number of electrode pads. The matrix wiring type LED array 110 is of the structure in which a high resistance substrate is divided electrically into M blocks by forming an element-separating region 111 and a p-type impurity is then diffused to form N LEDs 112 in each of the M blocks. The LED includes a p-type semiconductor diffusion region and corresponds to a light-emitting portion.
Each LED 112 is connected to a p-side electrode 113 and an n-side electrode 114. The n-side electrode 114 is common to all LEDs 112 in a corresponding one of M blocks. The p-side electrodes 113 in one of the M blocks are connected to corresponding p-side electrodes 113 in the other of the M blocks through corresponding ones of common wires 115. A p-side electrode pad 116 formed in each block is connected to a corresponding one of the common wires 115. An n-side electrode 114 in each block is connected to an n-side electrode pad 117 in the same block.
Thus, with the matrix wiring type LED array 110 of the aforementioned configuration, current is supplied to a desired LED in each block through the n-side electrode 117 and a corresponding p-side electrode 116, thereby energizing the desired LED.
With the aforementioned conventional matrix wiring type LED array 110, an element-separating region 111 has a certain width and extends straight across the width of the LED array 110. If the packing density of an LED array is to be increased, the distance between light-emitting portions (LED) requires to be shortened and therefore the width of the element-separating region 111 requires to be narrowed. In addition, the element-separating region 111 is quite long. Thus, merely increasing the density of conventional matrix wiring type LED array 110 increases the chance of the element-separating region ill being affected by particles 118 which are foreign materials produced during the manufacturing processes of semiconductor or entered from somewhere else. Particles 118 cause poor insulation between elements and are detrimental to pattern formation using a mask.
In other words, as shown in FIG. 6, when the width of the element-separating region 111 becomes very narrow, particles entering into the element-separating region connect electrically the adjacent blocks, being detrimental to the formation of good element-separating region as well as decreasing the manufacturing yield of array chips.
An object of the invention is to provide a light-emitting element array having an element-separating structure that can be manufactured with an increased density of light-emitting portions while also maintaining high chip yield.
A light-emitting array has a plurality of semiconductor diffusion regions aligned on a substrate. The semiconductor diffusion regions are formed in a semiconductor layer formed on the substrate by diffusing an impurity. The array includes the semiconductor layer of a first conductivity type and a predetermined number of semiconductor diffusion regions of a second conductivity type by diffusing the impurity. The array has an element-separating region that defines semiconductor blocks electrically isolated from one another, and the first conductive electrode formed in each of the semiconductor blocks. The substrate is made of a material that the plurality of semiconductor blocks can be electrically isolated. The element-separating region has a narrow portion only over a short distance.